In the construction of pipeline, it is common to position one end of a pipe section at the end of the pipeline under construction and weld the abutting ends together so that the pipe section becomes part of the pipeline. By moving the welding equipment along the pipeline as it is constructed, any desired length of pipeline can be created. However, one of the difficult problems in this type of operation is to ensure that the abutting ends of the pipe section and pipeline are properly positioned for welding. The center line of both the pipeline and pipe section at the weld should coincide. In addition, the ends of the pipeline and pipe section should be precisely aligned and have the proper gap between the adjacent pipes maintained to perform the weld.
In the past, both internal and external clamps have been used to align and clamp pipe for welding. Internal clamps are sometimes preferred due to the fact that they allow for uninhibited access to the exterior of the pipe joint for welding. U.S. Pat. No. 3,445,104, issued to E. H. Douglas on May 20, 1969, illustrates one example of an internal pipe clamp. In this device, two rings of clamp shoes are mounted on the clamp. The rings are spaced apart a predetermined distance along the length of the clamp. Each ring of shoes can be moved radially outward to clamp against the inner surface of a pipe section. The clamp is positioned within the pipe sections to be welded at the abutting ends of the pipe sections and each ring of shoes will be urged against the inner surface of a pipe section, drawing the abutting ends of the pipe into alignment for welding.
In some other internal pipe clamps, a back-up plate is employed to facilitate welding of the joint. For instance, U.S. Pat. No. 3,197,195, issued to J. S. and E. H. Work on Jul. 27, 1965, illustrates an internal pipe clamp which employs a back-up plate coupled to flanges adjacent to each side of the back-up plate, thereby allowing the pipe to be internally clamped by the single flange/back-up plate apparatus at the site of the pipe joint.
Another internal pipe clamp design is described in U.S. Pat. No. 3,920,171 to Edward A. Clavin, issued Nov. 18, 1975. In this clamping apparatus, the clamping mechanism has attached to it a means for properly spacing the ends of the pipes to be welded. This apparatus does not contain back-up plate nor does it clamp along substantially the entire internal pipe circumference, but rather it employs finger-like projections that contact the pipe at a number of locations.
In addition, when welding pipe of certain alloys, including for example stainless steel, the weld must be made in an oxygen free environment. Stainless steel and certain other alloys, oxidize when heated to the temperatures used in welding. If such oxidization occurs, the pipe will fail in service much more rapidly because of the corrosion that was created by the failure to weld the pipes in an oxygen free environment. In order to provide for the welding of pipe in a pipeline in an oxygen free environment, a technique has been developed to purge the oxygen from the weld site. One way this can be accomplished is by employing inflatable bladders within each of the pipe sections to be welded to define an enclosed volume within the pipe sections which can be purged with an inert gas, such as argon, thereby replacing the oxygen rich atmosphere and permitting the weld to be made by welding equipment outside the pipe. When employing such a purge system, the pipe sections are frequently aligned and clamped by an external clamping mechanism.
European Patent Application Publication No. 0193812 A2, published on Sep. 10, 1986, discloses an internal pipe clamp device which also contains a purge system. This apparatus contains two clamping rings for clamping the pipes near the pipe joint, as well as two sealing rings adjacent to the clamping rings and away from the pipe joint. Thus, these sealing rings define an enclosed area containing the clamping rings and the pipe joint. This apparatus does not include a back-up plate.
U.S. Pat. No. 5,609,291 to Jon C. Hummel, issued on Mar. 11, 1997, describes an internal pipe clamp which contains a groove that is to be oriented at the pipe junction. This groove contains holes through which purge gas is delivered to the weld area. This invention employs a double-wedge-type expansion system as opposed to a hydraulic piston-type expansion system. In addition, this invention does not provide a means for ensuring proper placement of the pipe junction or proper pipe junction spacing. Japanese Patent Application No. JP19940246841, published as Publication No. JP8090228, again describes an internal pipe clamp which contains a groove on the clamping shoes, the groove containing holes through which a purge gas is delivered to the weld area. However, this invention also fails to provide a means for ensuring proper placement of the pipe junction or proper pipe junction spacing.
Thus, a need still exists for a pipe clamping apparatus which is able to clamp and align two adjacent sections of pipe internally while providing a back-up plate for the weld, an inert gas purge at the weld site, and a means for ensuring the pipe junction is properly placed along the clamping apparatus and possesses the proper pipe spacing.